The present invention relates generally to medium voltage power controllers and, specifically, to medium voltage, solid-state, power controllers for a chiller or HVAC system. The term “power controller” as used herein can refer to either or both of starters and variable speed drives.
In low voltage chiller systems, the starter box for the compressor motor can be mounted directly on the chiller system as discussed in U.S. Pat. No. 4,895,005, which patent is hereby incorporated by reference. However, for a medium voltage chiller system, the power controller box, i.e., the starter box and/or the variable speed drive box, for the compressor is typically mounted on the floor either next to the chiller system or in a separate equipment room because of the larger size of the power controller box, which size can typically be greater than 100 cubic feet.
One of the reasons for mounting the power controller box on the floor for medium voltage chiller systems is that medium voltage can be up to forty to fifty times greater than low voltage. The larger voltages used in medium voltage applications can create a more difficult working environment because the electrical strike distance and creep distance are much longer than in a low voltage environment. The longer strike and creep distances require larger electrical spacings and the use of protective equipment for the mounting of components that result in a larger power controller box. In addition, the devices used for the medium voltage power controller box must be designed for the larger voltages associated with medium voltage, which also contributes to a larger power controller box. In other words, the physical size of the box or cabinet, as caused by electrical spacing, strike and creep distances and the need to cool the electrical components, may be significant.
One attempt that has been made to mount medium voltage starter components on a chiller system is described in U.S. Pat. No. 6,679,076 to Duga et al. The Duga et al. system discusses the use of two starter boxes mounted on the chiller system for specific sizes of chiller systems and with specific unit mounting locations. The two starter boxes in the Duga et al. system are interconnected by wiring and conduit. One major drawback of the two box arrangement in the Duga et al. system is that it involves complicated and expensive wiring arrangements in order to interconnect the starter boxes and the motor.
Therefore, what is needed is a medium voltage, solid-state power controller for a chiller system that can be mounted on or near the chiller system without an electrical conduit connection between the medium voltage motor and a box of the power controller.